<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>

    // function foo(x,y){
    //     y = y || 0;
    //     return x+y;
    // }
    //
    // console.log(foo(5));


    let foo = (x=1,y=1) => x+y;
    console.log(foo(5));

</script>

</body>
</html>